I have 78 300d with a turbo expansion tank radiator set up and I need help!

the car used to have the cap on the radiator it self but they don't re-make that style any more so went to the turbo style radiator. the expansion tank, nissen radiator, expansion tank hose, and thermostat (i have tested first before installed) is all new but the water pump is original from the car and radiator cap was replaced year ago from the original radiator.

the issue is the temp is at 200 F and never drops. it has heat from the heater, upper radiator is hot BUT the lower radiator is cold and has no pressure when i squeeze it and the t-stat housing get worm and hot back and forth. any one have a clue??? or is it normal???